1. Field of the Invention
This invention relates to an air bag apparatus mounted on a steering wheel, front instrument panel, front door trim or the like of an automobile. More particularly it relates to an apparatus for mounting and securing a pad cover onto and to a base plate mounted on a steering wheel, front instrument panel, front door trim or the like by way of a mounting plate or a like element.
The present invention relates also to a process for assembling an air bag apparatus for an automobile, and more particularly to an assembling method and an assembling apparatus for fastening a pad cover and a base plate of an air bag apparatus to each other.
The pad cover is generally referred to "module cover", "receiving cover, "lid", "cover door" or "deployment door" and is used as a case or housing for receiving an air bag or acting as cushioning.
2. Description of the Prior Art
Conventionally, a mounting apparatus for an air bag apparatus of the type mentioned for fixedly mounting on a base plate a pad cover in which an air bag, a gas generator and so forth are accommodated is disclosed, for example, in Japanese Patent Laid - Open Applications Nos. Showa 55-110643, Showa 63-184549 and Heisei 4-27639.
FIG. 25 shows the mounting apparatus disclosed in Japanese Patent Laid - Open Application No. Heisei 4-27639. Referring to FIG. 25, the mounting apparatus is applied to an air bag apparatus which includes an air bag 21 mounted on a mounting plate 23 and an air bag cover 24 which covers over the air bag 21. An upright portion 26 extends uprightly from a peripheral edge of a flat portion 23A of the mounting plate 23 on which the air bag 21, an inflator 22 and a retainer 18 (a ring - like element for securing the air bag 21 to the mounting plate 23) are mounted. A side circumferential wall 25 of the air bag cover 24 is contacted with and held against the upright portion 26 by a stiffening plate 12, and the elements are secured to each other by means of rivets 13 which extends through them. This particular mounting apparatus is called a "rivet type" mounting apparatus.
Meanwhile, FIG. 26 shows the mounting apparatus disclosed in Japanese Patent Laid - Open Application No. Showa 55-110643. Referring to FIG. 26, the mounting apparatus shown includes a mounting plate 23 to which a circumferential edge of a side circumferential wall 25 of an air bag cover 24, which covers the circumference of an air bag 21, and is snapped by means of a pawl plate 14 and a regulation wall 16 of the mounting plate 23. The pawl plate 14 has an arresting pawl 15 which is inserted in and engaged with an arresting groove 28 formed on an inner circumferential face of the side circumferential wall 25 of the air bag cover 24. The regulation wall 16 of the mounting plate 23 is inserted in an insertion groove 17 formed on a lower end face of the side circumferential wall 25 of the air bag cover 24. This particular mounting apparatus is called a "snap - in type" mounting apparatus.
With the conventional mounting apparatus for mounting a pad cover on a base plate described above, however, whether they are of the rivet type or the snap - in type, a plurality of plates or parts such as mounting plates or pawl plates are required and the structure of the apparatus is complicated. Consequently, the number of steps in production is great and the operability is low, and also the weight is great. As a result, a high cost of manufacture is required. Further, such a great weight of an air bag apparatus which is mounted at a central portion of a steering wheel of an automobile results in a great moment of inertia around the axis of the steering wheel and deteriorates the steering performance of the automobile.
Additionally, in the air bag apparatus described above, in order to fasten the pad cover to the base plate, the base plate and/or the pad cover are positioned using a robot which can operate in directions of two--or three--axes or are manually operated to secure them by means of rivets, bolts or some other suitable fastening members.
To this end, such rivets, bolts or some other fastening members must be inserted accurately into predetermined holes of the pad cover and the base plate. Accordingly, the operability in assembly to secure the quality assurance is low.